Wireless communication systems provide for radio communication links to be arranged within the system between a plurality of user terminals. Such user terminals may be mobile and may be known as ‘mobile stations’ or ‘subscriber units.’ At least one other terminal, e.g. used in conjunction with subscriber units, may be a fixed terminal, e.g. a control terminal, base station, repeater, and/or access point. Such a system typically includes a system infrastructure which generally includes a network of various fixed terminals, which are in direct radio communication with the subscriber units. Each of the base stations operating in the system may have one or more transceivers which may, for example, serve subscriber units in a given local region or area, known as a ‘cell’ or ‘site’, by radio frequency (RF) communication. The subscriber units that are in direct communication with a particular fixed terminal are said to be served by the fixed terminal. In one example, all radio communications to and from each subscriber unit within the system are made via respective serving fixed terminals. Sites of neighboring fixed terminals in a wireless communication system may be offset from one another or may be non-overlapping or partially or fully overlapping. In another example in which subscriber units can operate in a direct mode (e.g., without having to pass through a repeater or base station), a fixed terminal such as a control terminal may provide for a mechanism to update the direct mode subscriber units with new program settings, channels, groups, etc.
Wireless communication systems may operate according to an industry standard protocol such as, for example, the Project 25 (P25) standard defined by the Association of Public Safety Communications Officials International (APCO), or other radio protocols, such as the TETRA standard defined by the European Telecommunication Standards Institute (ETSI), the Digital Private Mobile Radio (dPMR) standard also defined by the ETSI, or the Digital Mobile Radio (DMR) standard also defined by the ETSI. Communications in accordance with any one or more of these standards, or other standards, may take place over physical channels in accordance with one or more of a TDMA (time division multiple access), FDMA (frequency divisional multiple access), or CDMA (code division multiple access) protocols. Subscriber units in wireless communication systems such as those set forth above send user communicated speech and data, herein referred to collectively as ‘traffic information’, in accordance with the designated protocol.
Many so-called “public safety” wireless communication systems provide for group-based radio communications amongst a plurality of subscriber units such that one member of a designated group can transmit once and have that transmission received by all other members of the group substantially simultaneously. Groups are conventionally assigned based on function. For example, all members of a particular local police force may be assigned to a same group so that all members of the particular local police force can stay in contact with one another, while avoiding the random transmissions of radio users outside of the local police force.
Similar wireless communication systems may be used at mining sites, where events such as blasting operations impart unique requirements on the wireless communication system supporting the mining operation across one or more mining sites. Conventional methods of signaling events such as blasting amongst subscriber units have typically relied upon an assignment of a separate RF channel over which predefined analog audio is mixed at the infrastructure and broadcast from the fixed terminal to the subscriber units, and played back at the subscriber units that are tuned to the separate RF channel, to indicate the respective situation.
However, with the recent advent of digital radio systems, the conventional analog methods can either no longer be used or have become prohibitively expensive to implement in terms of cost and system resources. Accordingly, a system and method is needed for digital two-way radio systems to allow for continuous, periodic, or semi periodic tones to be mixed with digital audio and played back at subscriber units across one or more sites to indicate a respective situation, and a system and method to allow subscriber units to initiate the play back of the continuous, periodic, or semi periodic tones, without unnecessarily impacting network bandwidth or frequency channel availability, and while making allowances for calls existing at the time of the initiation of the continuous, periodic, or semi periodic tone to continue.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present disclosure.